1. Field of the invention
The present invention relates to a magnetic head device for recording and reproducing signals such as image signals on and from a magnetic recording medium, and more particularly to an improved magnetic head device employing a thin-film magnetic recording and reproducing head.
2. Description of the Prior Art
Various magnetic recording and reproducing apparatus have heretofore been developed for recording and reproducing various kinds of signals on and from magnetic recording mediums. The magnetic recording and reproducing apparatus mostly incorporate a magnetic head device having a positioning member for keeping the magnetic head in good contact with the magnetic recording medium. As recent years have seen miniaturization and diversification in the shape of magnetic recording mediums, efforts have been made to develop magnetic heads suitable for use with a variety of smaller magnetic recording mediums. For example, there is known a small-size disc-shaped magnetic recording medium in which the innermost circular recording track has a radius of 15 mm and the outermost circular recording track has a radius of 20 mm. Assuming that this magnetic recording medium rotates at 3,600 r.p.m. for recording and reproducing one field of video signals per revolution, and that the signals are recorded on the medium across 60 micrometers/track, then taking into account the presence of a guard band, etc., signals can be recorded on a total of 50 tracks, and hence 50 fields of image signals can be recorded on the medium. When recording and reproducing the image signals on and from the magnetic recording medium, the magnetic head used therewith is fed radially across the medium intermittently at a pitch of 100 micrometers.
For recording signals in frames on such a discshaped magnetic recording medium or sheet, there are two methods available: (1) the magnetic recording sheet is rotated at 1,800 r.p.m., and (2) two magnetic heads are switched over for recording and reproducing alternate fields. Since the signal packing density required prevents the magnetic sheet from being rotated at a lowered speed, however, two magnetic heads are normally employed for recording signals in frames. Conventionally the two magnetic heads are bulk heads made of a bulk-type magnetic material. Each bulk head is relatively large in size, i.e., about 2.times.2.times.0.5 mm including the winding. Therefore, two bulk heads cannot be used with respect to a magnetic recording medium of the type described above which has a track pitch of 100 micrometers. There is also known a two-channel bulk magnetic head of a small-size unitary construction but this cannot be mass-produced efficiently because of difficulty in machining and a low yield rate. The two-channel bulk magnetic head also has the problem of crosstalk between the channels.
For the reasons described above, the trend in the art is toward thin-film two-channel magnetic heads instead of the two-channel bulk magnetic heads. However, the thin-film magnetic head has a poor recording efficiency since it is difficult to achieve an increased number of winding turns in the thin-film fabrication process. For example, a magnetic recording medium having a metallic coating for recording video signals thereon has a high coercive force, and for magnetization requires a magnetomotive force at least four times as large as the magnetomotive force required to magnetize ordinary magnetic recording mediums with coatings of iron oxide. The magnetomotive force is expressed as the product of the number N of winding turns and the recording current I. Since it is difficult to increase the number N of winding turns in the thin-film magnetic head, the recording current I should be increased for a higher recording efficiency. However, as the recording current is increased, the power consumption is also increased at the time of recording signals, and hence the magnetic head is heated to a higher temperature. The magnetic material on the magnetic medium tends to be deteriorated by contact with the heated magnetic head, resulting in a reduced recording efficiency. Other problems with the thin-film two-channel magnetic head are that the winding, which is of a reduced thickness, is liable to be cut off due to the heat generated by the increased recording current, and the crosstalk between the channels is increased in proportion to the recording current.